What’s the best way to connect with Millennials who are interested in politics? As the Democratic and Republican U.S. presidential candidates continue to aggressively court Americans, this question is vexing quite a few campaigns.

While emerging social media platforms are clearly one way connect with these younger voters—which is why even Bernie Sanders is now Snapchatting—one of the most effective channels may actually be one of the oldest: music.

To be sure, these Millennials (aged 18-34) are not easy to reach. This group is more multicultural and educated compared to earlier generations. And they have a wide-range of eclectic tastes that often make both traditional and experimental outreach efforts ineffective.

However, approaching this group appropriately can have a huge payoff. Millennials comprise a quarter of the U.S. population, and nearly three-quarters (73%) say they have some affiliation with a political party.

Overall, according to the Millennial Music Listener Audience Insights report, Millennials are almost twice as likely to be Democrats than Republicans (32% vs. 17%), but large segments also either identify as independents (24%) or as indifferent/unaffiliated (23%). In other words, they represent large, important blocks of both affiliated and undecided voters.

So why is music such a powerful way to engage these political Millennials?

Previous Nielsen research has found that including music in messaging increases effectiveness across four key metrics: creativity, empathy, emotive power and information power.

Moreover, music is already an integral part of most Millennials’ lives. The group spends more money attending live events compared with other age groups and is more likely to attend every type of live music event (concerts, festivals, live music sessions at clubs/bars or club events with or without a headlining DJ).

Social media plays an important role in live music discovery for Millennials, as it does in many parts of their lives. And more than half of Millennials who attend live music events say they use social networks to uncover new events.

While digital channels have a big impact, traditional radio remains influential as well: 58% of Democrat Millennials, 68% of Republican Millennials, and 56% of independent and unaffiliated Millennials say they discover new music via FM, AM or satellite radio.

Which musicians do Millennials connect with? Katy Perry is a key tastemaker; according to Nielsen N-Score data, she ranks among the top five music personalities with adults age 18-34. That may explain why Hillary Clinton recently brought her onstage at a rally in Iowa.

Republican candidates have music star fans as well. Kid Rock may be the most visible, having appeared on Fox News way back in 2013 to publically give Ben Carson a shout-out. Pitbull has said he “chills” with both Marco Rubio and Jeb Bush, though he hasn’t endorsed either yet. It appears that Pit—like many Millennial voters—is still undecided.